TY - JOUR
T1 - Changes in muscle size, architecture, and neural activation after 20 days of bed rest with and without resistance exercise
AU - Kawakami, Yasuo
AU - Akima, Hiroshi
AU - Kubo, Keitaro
AU - Muraoka, Yoshiho
AU - Hasegawa, Hiroshi
AU - Kouzaki, Motoki
AU - Imai, Morihiro
AU - Suzuki, Yoji
AU - Gunji, Atsuaki
AU - Kanehisa, Hiroaki
AU - Fukunaga, Tetsuo
N1 - Funding Information:
Acknowledgement The authors thank Dr. Y. Makita and the staff in Makita Hospital for assistance with the MRI procedure. This study was funded in part by Ground Research for Space Utilization, promoted by the National Space Development Agency and Japan Space Forum.
PY - 2001
Y1 - 2001
N2 - Nine healthy men carried out head-down bed rest (BR) for 20 days. Five subjects (TR) performed isometric, bilateral leg extension exercise every day, while the other four (NT) did not. Before and after BR, maximal isometric knee extension force was measured. Neural activation was assessed using a supramaximal twitch interpolated over voluntary contraction. From a series cross-sectional magnetic resonance imaging scans of the thigh, physiological cross-sectional areas (PCSA) of the quadriceps muscles were estimated (uncorrected PCSA, volume/estimated fibre length). Decrease in mean muscle force after BR was greater in NT [-10.9 (SD 6.9)%, P < 0.05] than in TR [0.5 (SD 7.9)%, not significant]. Neural activation did not differ between the two groups before BR, but after BR NT showed smaller activation levels. Pennation angles of the vastus lateralis muscle, determined by ultrasonography, showed no significant changes in either group. The PCSA decreased in NT by -7.8 (SD 0.8)% (P < 0.05) while in TR PCSA showed only an insignificant tendency to decrease [-3.8 (SD 3.8)%]. Changes in force were related more to changes in neural activation levels than to those in PCSA. The results suggest that reduction of muscle strength by BR is affected by a decreased ability to activate motor units, and that the exercise used in the present experiment is effective as a countermeasure.
AB - Nine healthy men carried out head-down bed rest (BR) for 20 days. Five subjects (TR) performed isometric, bilateral leg extension exercise every day, while the other four (NT) did not. Before and after BR, maximal isometric knee extension force was measured. Neural activation was assessed using a supramaximal twitch interpolated over voluntary contraction. From a series cross-sectional magnetic resonance imaging scans of the thigh, physiological cross-sectional areas (PCSA) of the quadriceps muscles were estimated (uncorrected PCSA, volume/estimated fibre length). Decrease in mean muscle force after BR was greater in NT [-10.9 (SD 6.9)%, P < 0.05] than in TR [0.5 (SD 7.9)%, not significant]. Neural activation did not differ between the two groups before BR, but after BR NT showed smaller activation levels. Pennation angles of the vastus lateralis muscle, determined by ultrasonography, showed no significant changes in either group. The PCSA decreased in NT by -7.8 (SD 0.8)% (P < 0.05) while in TR PCSA showed only an insignificant tendency to decrease [-3.8 (SD 3.8)%]. Changes in force were related more to changes in neural activation levels than to those in PCSA. The results suggest that reduction of muscle strength by BR is affected by a decreased ability to activate motor units, and that the exercise used in the present experiment is effective as a countermeasure.
KW - Countermeasure
KW - Pennation angle
KW - Physiological cross-sectional area
KW - Twitch interpolation
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U2 - 10.1007/s004210000330
DO - 10.1007/s004210000330
M3 - Article
C2 - 11394257
AN - SCOPUS:0035115772
SN - 1439-6319
VL - 84
SP - 7
EP - 12
JO - European Journal of Applied Physiology
JF - European Journal of Applied Physiology
IS - 1-2
ER -
